JPH0373819A - Magnetostriction type torque detector - Google Patents

Abstract

PURPOSE:To remove an error in torque detection by driving an AC demagnetizing circuit after ending torque measurement to demagnetize a shaft to be measured. CONSTITUTION:A demagnetizing coil 15 is arranged on the outside of sensor coils 13a, 13b arranged around the shaft concentrically with the shaft. The coil 15 is connected to the AC demagnetizing circuit 16 to execute demagnetizing operation only after ending the torque measurement. The circuit 16 is constituted of e.g. PTC thermistors 21A, 21B and a switch 22 connected between a power supply 20 and the coil 15. Since the thermistors 21A, 21B have characteristics increasing their resistance values in accordance with temperature rise, a demanagetizing current value to be impressed to the coil 15 is gradually attenuated in accordance with the lapse of energizing time. When the switch 22 of the circuit 16 is turned of after ending the torque measurement, the attenuated current is impressed to the coil 15 by the action of the thermistors 21A, 21B, so that the coil 15 demognetizes magnetism left in the shaft 10 to be measured. Thus, the shaft is demagnetized by generating an AC magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a magnetostrictive torque detector that measures the torque of a rotating shaft using the magnetostrictive effect.

(Prior art) The 812th torque detector using the magnetostrictive effect
I, there is something like the one shown in No. 9121 (Japanese Unexamined Patent Publication No. 1986-
(See Publication No. 185136).

This magnetostrictive torque detector uses a material having a magnetostrictive effect as the shaft 10 to be measured, such as Fe-13 weight % A1 alloy or steel for machine structural use (SCM, SNCM, etc.), and has a shaft surface aligned with the shaft center line 10a. Spiral grooves 11a, 1 lb formed at an angle of ±45 degrees and arranged at equal intervals in the circumferential direction,
The magnetic anisotropy portions 12a and 12b are formed symmetrically on the left and right sides to form geometrically magnetic anisotropic portions 12a and 12b due to the skin effect of magnetic permeability.

Two sensor coils 13a and 13b are installed on the outer periphery of the shaft 10 to be measured with a predetermined gap between each spiral groove 11a and l.
Place it so that the center matches lb.

As shown in FIG. 9, these sensor coils 13a and 13b are connected to form a bridge circuit with resistors 14a and 14b, and one of the opposing connection points CD is connected to the supply side (Vin) of the AC power source 15. Output 1 between the other connection point A and B
1! (Vd=Vb-Va).

In this way, a magnetic circuit passing through the shape magnetic anisotropic portions 12a, 12b formed by the spiral grooves 11a, llb is formed around both sensor coils 13a, 13b, respectively.

Now, when a clockwise twisting torque is applied to the shaft 10 to be measured, the magnetic anisotropic portion 12a formed by one spiral groove 11a undergoes tensile deformation, and the other spiral groove 11b
The magnetically anisotropic part 12+3 formed by is subjected to compressive deformation.

At this time, if the magnetostriction constant of the shaft 10 to be measured is λnO, the magnetic permeability increases with tensile deformation and decreases with compressive deformation. As a result, the inductance la of one sensor coil 13a increases, and the inductance Lb of the other sensor coil 1313 decreases. Measured axis 10
When a counterclockwise wajiritorku (= is added to), the result is the opposite.

Therefore, the AC power supply 15 provides a constant AC voltage (Vi
When a twisting torque T is applied to the shaft 10 under test while applying voltage Vd(n), the output voltage Vd(
= Vb-Va) is obtained as follows.

Vd=fib-Ra+(Lb-La)S)Ro-Vin
.

<Ro+Ru+5La) (Ro+Rb→-3Lb) In this way, the output voltage changes according to 1 herk of twist, and the torque applied to the shaft 10 to be measured can be measured.

(Problem to be Solved by the Invention) However, in such a magnetostrictive torque detector, the magnetic properties of the shaft to be measured tend to change over time due to the magnetization history and stress history of the shaft to be measured. There was a problem in that the sensitivity became unstable and the torque detection accuracy decreased.

Generally, AC demagnetization is sometimes used to remove the residual magnetism of a magnetized magnetic material, but when this is applied to a magnetostrictive torque detector, the heat generated during AC demagnetization passes through the magnetic anisotropic part of the measured axis. This may change the magnetic property and reduce the accuracy of l-lux measurement.

When a magnetic body is periodically magnetized by an AC magnetic field during AC demagnetization, the magnetic domain direction of the magnetic body changes each time, generating heat accompanied by energy loss (so-called hysteresis loss). When a temperature gradient occurs in the axial direction of the measurement axis and a temperature difference occurs between the two magnetically anisotropic parts, the magnetic permeability of each changes, causing fluctuations in the measurement output even if the torque does not change.

Therefore, if AC demagnetization is performed without limit, the accuracy of the torque detector becomes unstable.

The present invention aims to solve such problems.

<Means for Solving the Problems> Accordingly, the present invention provides a shaft to be measured having a magnetostrictive effect in which a magnetic anisotropic portion forming a predetermined angle with respect to the axis is provided on the peripheral surface of the shaft, and a shaft to be measured. a sensor coil placed near the sensor coil, a magnetic circuit formed in such a way that the magnetic flux generated by the sensor coil passes through the magnetic anisotropic part, and a magnetic circuit that changes according to the magnitude and direction of the torsional torque applied to the shaft to be measured. In a magnetostrictive torque detector that detects torque from changes in the output of a magnetic circuit based on the magnetic permeability of a magnetically anisotropic part, a degaussing coil is arranged concentrically with respect to the axis to be measured, and the degaussing coil is It is equipped with an AC degaussing circuit that operates 11 times after the torque measurement is completed.

(Function) Therefore, when the AC degaussing circuit operates the degaussing coil after completing torque measurement, the residual magnetism of the shaft to be measured is removed.
The magnetic properties are stabilized, and changes over time in the sensitivity of the torque detector can be reduced.

Also, since AC demagnetization operation is not performed during torque measurement,
Even if a temperature difference occurs in the magnetically anisotropic portion of the shaft to be measured during demagnetization, it has no bearing on measurement accuracy and does not cause measurement errors.

(Example) Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 1, a degaussing coil 15 is disposed concentrically with the shaft 10 to be measured further outside the sensor coils 13a, 13b arranged around the shaft 10 to be measured. This demagnetizing coil 15 is connected to an AC demagnetizing circuit 16, so that demagnetizing operation can be performed only after torque measurement is completed.

For example, as shown in FIG.
The PTC thermistor 2LA, 21B, a switch 22, etc. are interposed between the degaussing coil 15 and the degaussing coil 15.

The PTC thermistors 21A and 21B have a characteristic that the resistance value increases as the temperature rises, and as a result,
As shown in FIG. 3, the value of the demagnetizing current applied to the demagnetizing coil 15 gradually attenuates as the energization time passes.

Note that the maximum current value at the initial stage of operation is set so that the degaussing coil 15 generates a magnetic field greater than the coercive force remaining in the shaft 10 to be measured.

The switch 22 can be turned on after completion of the torque measurement. For this purpose, for example, the switch 22 can be turned on only when the main power source of the torque detector is off.

Therefore, when the switch 22 of the AC degaussing circuit 16 is turned on after the torque measurement is completed, the PTC thermistor 21A,
21B, a damping current as shown in FIG. 3 is applied to the degaussing coil 15.

As a result, the degaussing coil 15 generates an alternating current magnetic field that erases the remaining magnetism in the shaft 10 to be measured, thereby making it possible to demagnetize the shaft 10 to be measured.

By performing demagnetization in this manner, the magnetic characteristics of the shaft 1o to be measured are stabilized, and the sensitivity at the time of ■·Luke measurement is stabilized.

Next, in the embodiment shown in FIG. 11, an automatic stop circuit 17 is added to automatically stop the operation of the AC degaussing circuit 16.

As shown in Fig. 5, this automatic stop circuit 7 is an AC degaussing circuit 1 that turns off the main power supply of the torque detector.
6 is turned on to start the operation, and when the value of the degaussing current flowing through the AC degaussing circuit 16 becomes less than a predetermined value, for example lon+8, the switch of the AC degaussing circuit 16 is turned OFF and the operation is automatically stopped. (Steps 51 to 55).

Note that the current value is read after a predetermined time has elapsed after the start of operation, but this is because the initial value is zero, and the point is that it does not need to be done at the same time as the start of operation of the AC demagnetizing circuit 16.

As the demagnetizing current detection means 24 of the AC demagnetizing circuit 16,
For example, it includes a current transformer.

FIG. 6 shows another embodiment of the automatic stop circuit 17, in which the ON time of the torque detector main power supply is accumulated by a timer, and when the accumulated time exceeds a predetermined value, for example 8 hours, AC demagnetization operation is performed. As a result, AC demagnetization can be automatically performed at regular intervals so that the torque detection sensitivity does not become unstable (steps 61 to 63). Note that the subsequent steps 64 to 69 are demagnetizing operations similar to steps 51 to 55 described above.

Note that the timer for calculating the cumulative time may be reset when the AC degaussing circuit is stopped.

Further, in the embodiment shown in FIG. 7, when this cumulative time exceeds a predetermined value, an alarm is issued to prompt AC demagnetization operation.

In other words, when the main power of the torque detector is turned on when the cumulative time exceeds a predetermined value, the rotation speed of the measured shaft is read, and when the rotation speed is zero, the main power is forcibly turned on. The AC demagnetization operation is started by turning off the rotation speed, and when the number of revolutions is not zero, a demagnetization alarm is lit to prompt the demagnetization operation (steps 74 to 78). The rest is the same as the 612I embodiment.

(Effects of the Invention) As described above, according to the present invention, the AC degaussing circuit is operated to demagnetize the shaft to be measured after torque measurement is approved, so that the magnetic characteristics of the shaft to be measured are always stable. become,
The time-dependent change in the sensitivity of the torque detector (f) is reduced to eliminate errors in torque detection accuracy, and since the demagnetization operation using the AC magnetic field is performed except for torque Jtl + constant time, the heating effect of the measured shaft that occurs during demagnetization is reduced. does not adversely affect the measurement function of the torque detector.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of an AC degaussing circuit, and FIG. 3 is an explanatory diagram showing a demagnetizing current waveform.
Figure 4 is a circuit diagram showing another embodiment of the AC degaussing circuit;
7 to 7 are flowcharts showing the control operation of each embodiment of the automatic stop circuit. FIG. 8 is a sectional view of a conventional example, and FIG. 9 is a detection circuit diagram as well. 10... Axis to be measured, 2a, 1 2b... Magnetic anisotropy section, 13b... Sensor coil, 15... Demagnetizing coil, 6... AC demagnetizing circuit, 7... Automatic stop circuit. 2nd Figure 12a, 12b-J4 quirk 5. l feng t513a13b-
--enM Coil 15-5 Port Coil Fig. 7 Fig. 8 Fig.

Claims (1)

[Claims] A measured shaft with a magnetostrictive effect in which a magnetic anisotropic part forming a predetermined angle with respect to the shaft center is provided on the shaft circumferential surface, a sensor coil placed near the measured shaft, and the magnetic flux generated by the sensor coil. a magnetic circuit formed in such a way that it passes through the magnetically anisotropic part, and a change in the output of the magnetic circuit based on the magnetic permeability of the magnetically anisotropic part, which changes depending on the magnitude and direction of the torsional torque applied to the shaft to be measured. A magnetostrictive torque detector configured to detect torque from the shaft, characterized by comprising a degaussing coil arranged concentrically with respect to the axis to be measured, and an AC degaussing circuit that activates the degaussing coil after torque measurement is completed. Magnetostrictive torque detector.